The vast majority of Internet traffic uses stream-based transport protocols such as Transmission Control Protocol (TCP) or Stream Control Transmission Protocol (SCTP). Due to the growing number of end hosts such as smartphones and tablets, which are multi-horned, a variety of protocols have been proposed to improve end-to-end throughput or to enhance connection resilience. Examples for such protocols are Multipath TCP (MPTCP), Multi-connection TCP (MCTCP) and Concurrent Multipath Transfer SCTP (CMT SCTP).
Currently, multipath protocols can only be used if they are supported by both endpoints or hosts associated with the connection. This restriction obstructs deployment of multipath protocols since there is little incentive to upgrade an existing host unless all its potential peers are upgraded as well.
Solutions on layer 3 (L3) consist of Home Agent (HA) in Mobile IP, Packet-Data Node Gateway (PDN-GW) in LTE, GPRS Gateway Support Node (GGSN) in Universal Mobile Telecommunications System (UMTS). These functions apply tunneling mechanisms to switch between multiple paths. However, while these mechanisms permit rather inexpensive processing, they are not compliant with various middlebox requirements since the tunnel does not use stream-based protocols. These solutions further do not support multipath operation.
Solutions on layers 5-7 (L5-7) consist of Session Initiation Protocol (SIP) B2B proxies. However, such proxies do not permit seamless handover or multipath operation. They further restrict usage to applications that are specifically designed and developed for SIP.
Solutions on layer 4(L4) consist of brute force resource and memory intensive packet relay techniques in which multiple traffic subflows are assembled into a single traffic flow for use by a single path protocol, while single traffic flows are segmented into multiple traffic subflows for use by a multipath protocol. This process requires large amounts of buffer space and processing power to perform the assembly and segmentation functions, as well as store resulting traffic segments until such time as the safe delivery of the many packets forming the various traffic segments is acknowledged by the destination endpoint such that the packets may be discarded from the buffers. As such, network-hosted relay solutions have been found to be uneconomical.